Aircraft engine monitors for sensing and displaying various aircraft turbine engine performance related parameters are well known. Traditionally, the aircraft pilot was expected to monitor and record these parameters as they appeared on the cockpit instruments to determine when the parameter values exceeded predetermined limits. These records made by the aircrews were later reviewed by ground personnel to diagnose the condition of the aircraft turbine engine and to predict possible engine failures.
Aircrews normally monitored the cockpit instruments during starts, operation, and controlled maintenance tests. Aircrews may err in recording cockpit instrument values and fail to detect subtle changes in the cockpit instruments especially at low engine power. Aircrew monitoring is less effective in other than controlled conditions, such as at less than maximum rated power, since the pilot had no reference from which to detect the subtle changes in performance parameters. Aircrews had to have particular knowledge of the sophisticated operation of the turbine engine and the significance of the changes in the turbine engine performance parameters with respect to engine operation to be able to recognize which value changes were critical to diagnosing the engine performance. Further, even if the parameter values were accurately recorded, ground maintenance crews using the recorded parameters to diagnose the engine condition required keen knowledge of the operation of the turbine engine to interpret the recorded parameters during their engine performance diagnosis. The maintenance crews erred, if at all, on the side of safety by authorizing the complete overall of an engine when the pilots recorded unusual or out-of-limit parameter values. While this resulted in few engine failures, the extra caution often resulted in the unnecessary removal of good components during the overhaul of engines requiring minor or no repairs rather than a complete overhaul.
The traditional methods of recording engine performance parameters was thus incomplete and error prone and the traditional method of engine diagnosis and maintenance was overly cautious and costly.
Known electronic monitors of engine parameters, such as the Portable Engine Analyzer Test Set (PEATS) manufactured by Howell, Instruments, U.S. Ser. No. 036,903, now abandoned do provide memory and display of current aircraft performance parameter values. These monitors may be used in conjunction with manufacturers' lists identifying permissible individual parameter values at the maximum rated engine power to provide an indication of engine condition. The PEATS disclosed in U.S. Ser. No. 036,903 does not, however, allow the pilot and maintenance crews to instantaneously obtain a diagnostic value immediately indicative of engine condition while in flight or while operating at less than maximum power.